Selective bird feeders are well known in the art and are designed to limit the maximum size of a bird or animal which can access the seed in the feeder. The reasons for excluding certain birds may be many. Thus, as disclosed in U.S. Pat. No. 3,241,525, there is provided a selective bird feeder which is specific to cardinals. As taught by this patent, a favourite seed of cardinals is a sunflower seed; this seed is also popular with both smaller and larger birds.
Some larger birds will also access the seed within a bird feeder and many such birds, such as crows, grackles, blue jays and the like are considered by some people to be undesirable.
A further problem associated with bird feeders is marauders which gain access to the seeds. In particular, squirrels are well known for their ability to reach the seed in a bird feeder and to devour the same. Many approaches have been tried to discourage or prevent squirrels from reaching the bird feeder, including various types of covers and baffles on poles. These seldom work as squirrels have shown great ingenuity in overcoming such devices.
There are also many proposals in the art for squirrel proof bird feeders which utilize a shroud to cover openings in the side wall of a seed container. The shroud is biased to a first position, usually by a spring member, such that when weight is placed on the shroud, it moves to cover the feed openings. Thus, reference may be had to U.S. Pat. Nos. 5,445,109 and 6,945,192 which disclose such arrangements.
While such shroud type squirrel proof bird feeders are useful, they are relatively costly to manufacture and assemble due to different requirements such as maintaining the openings in the shroud and openings in the side wall of the seed container in alignment. One must also take into account inclement weather which can affect the functioning of the bird feeder.